ON COMETS. 113 



disturbances do really exist, and have often very con- 

 fiderable effects on the return of comets. This very 

 comet, in the table of its returns set down in the note 

 below,* offers some striking examples. There occurs, for 

 instance, 1378 A.D. and not 1380 set down for one of the 

 epochs of its appearance, with 78 years interval between 

 that and 1456. The fact is that Halley was mistaken in 

 supposing either the comet of 1305 or that of 1380 to be 

 the same with that in question. That comet really ap- 

 peared in 1378, but that fact Halley had no means of know- 

 ing. It has very lately come to light on searching the 

 Chinese annals. And the same annals have informed us 

 of no less than six other still more ancient appearances 

 of this selfsame comet, the earliest in the nth year be- 

 fore our Saviour. And this, it must be allowed, greatly 

 tends to increase our confidence in those venerable re- 

 cords of Chinese history. All this apparent irregu- 

 larity is owing to the action mainly of Jupiter, which is 

 a general disturber of comets, and gives a vast deal of 

 trouble to calculators, as I shall soon explain; and 

 Saturn is not without a finger in the pie. 



(23.) This prediction of Halley' s, as the time for its 

 accomplishment drew near, created a great sensation all 

 the astronomers furbished up their telescopes, and all 

 the mathematicians set to work to calculate. The 

 mutual actions of the planets in that long interval had 

 been well studied, and it was clearly ascertained that 



* A.D. 451, July 3 ; 760, June 11 ; 1378, Nov. 8 ; 1456, Tune 8 : 

 1531, Aug. 24; 1607, Oct. 26; 1682, Sept. 14; 1759, March 12 ; 

 1835, Nov. 15. 



II 



